Sunglasses are widely recommended and used when individuals are in direct or indirect sunlight. The protective effect provided by sunglasses is important to mitigate the health risks associated with overexposure of the eyes to sunlight, particularly the ultraviolet (UV) component thereof. It is well known that overexposure to ultraviolet radiation from the sun can cause or exacerbate cataracts, for example.
Another problem arises due to the glare from direct or reflected sunshine with most outdoor activities. Sunglasses are critical in minimizing glare from sunlight or reflected surfaces. Driving, boating, flying or just general activities in bright sunlight often cannot be safely performed without sunglasses.
Another feature that is typical of many wearers of sunglasses is the stylistic or aesthetic look of the sunglasses. Sunglasses are often considered a fashion accessory as well as utilitarian item. Thus, the style of the sunglasses may be as important as the relevant health mitigation that the sunglasses may provide.
Prescription sunglasses are often worn by people who have deficiencies in their vision. Many people suffer from eye problems, such as myopia, presbyopia or astigmatism that require corrective eyewear. Often, the corrective eyewear is incorporated into sunglasses. Such prescription sunglasses provide not only the health benefits from overexposure to sunlight, but also correct the eyesight of the wearer.
However, a problem often arises with people who may want to read or perform activities that require a change in their prescriptive eyewear. Many people have differing corrective vision requirements for far distance and near distance viewing. Often, multifocal eyewear lenses are provided for this need. Multifocal eyewear lenses are defined as lenses that include two or more regions or lens portions and where at least one of those regions has a magnified focal power. Multifocal lenses include bifocal lenses where at least one portion is magnified and the other portion has a differing focal power such as piano (non-magnified) or else magnified or otherwise adjusted to corrective the wearer's vision. Multifocal lenses may also include trifocal, progressive addition or any other type of eyewear lenses that has at least one portion that is intended for corrective vision purposes.
Bifocal eyewear provides a region in the upper and/or central region of the eyeglasses that is either piano or has a corrective focal power for far distance viewing and a lower region having a magnified focal power for near viewing needs. Other types of multifocal lenses may be used for other vision requirements, such as trifocal lenses. Another lens type is for people that suffer only from presbyopia. Presbyopia is the inability of the eye to focus at objects up close, generally within 36 inches. This individual has a choice of using a single magnification throughout the entire lens that allows them to read close up or have a bifocal at the bottom of the lens coupled with a non magnified upper area (called piano) of the lens. These glasses are called reading glasses and do not require prescriptions.
While this is more than adequate for indoor and night use, there is often a need for multifocal eyewear in direct sunlight. For example, many people enjoy reading or other activities that require near vision while on the beach or otherwise outdoors. Another example for such needs includes outdoor equipment operators, such as boating, that requires viewing of displays, maps and other near vision requirements while requiring non magnified (piano) far vision viewing for the full operation of the equipment.
One solution in satisfying this need is people may use a clip-on sunglass over the top of their existing bifocals or full lens reading glasses. Problems arise with the use of clip-on sunglasses however. It requires a separate purchase and clip-on's are not readily available in the style of the glasses they need to work with. Another problem is the attachment mechanism of the clip-on sunglasses to the bifocal eyewear. These attachment mechanisms tend to easily become disengaged at inopportune times. Another problem is that the eyewear becomes top heavy, unbalanced and cumbersome. Yet another problem is that the clip-on sunglasses destroy the aesthetic appeal of the eyewear.
There have been some attempts in the past to provide bifocal sunglasses. These attempts have created a relatively unattractive design. The bifocal sunglasses are readily evident by casual observation by the line of demarcation between the differing focal regions. Since sunglasses tend to be selected for stylistic reasons first and then health reasons, sunglasses with bifocals have not been popular in the past. Also, many people prefer that their vision deficiencies not be readily noticeable.
Previous bifocal sunglasses have a three-dimensional appearance. This look is due to the addition of a bifocal lens adhered either onto the inner surface or the outer surface of the sunglasses. These bifocal sunglasses are easily noticeable to the casual observer. As such, these sunglasses are undesirable to most individuals.
Thus the need exists for multifocal sunglasses that are not distinguishable from other sunglasses and particularly for bifocal sunglass lenses which have a magnified portion on the bottom with a non-magnified lens on top.